Concrete, which can withstand enormous compressive forces, is frequently combined with steel, which can withstand enormous tensile forces to produce a combined construction element that has the best properties of both materials. Thus it is known to fill a tube or the like with concrete to greatly increase its strength, or to embed reinforcing bars or members in a beam of concrete so as to increase the strength of the concrete beam.
It is also known to increase the fire resistance of a steel or other metallic structural member by covering it with concrete. The concrete acts as a fire-resistant insulator and therefore retards heat transmission to the steel beam embedded in the concrete so that the considerable loss in strength encountered in a fire is at least postponed. This fireproofing is typically carried out by simply spraying the steel structural member after installation with concrete, a procedure which also increases the beam's resistance to corrosion due to the basicity of the concrete coating.
Such arrangements have considerable problems though. First of all the concrete used for fireproofing typically acts merely as dead weight on the beam it is applied to. This concrete has in effect no load-bearing action. Furthermore, if the concrete fireproofing is applied prior to installation a good chance of chipping at least some of it off during handling is encountered. The bonding of the concrete to the steel member can also be problematic, in particular when the thus coated beam is subject to considerable thermal expansion and contraction, as is the case prior to integration into a larger structure.